their edges; and it is continually being moved about from some of them to others. No advantage is gained. It is simply that the tongue's position renders perpetual exploration almost inevitable; and by perpetual exploration is developed this unique power of discrimination. Thus the law holds throughout, from this highest degree of perceptiveness of the tongue-tip to its lowest degree on the back of the trunk; and no other explanation of the facts seems possible.
"Yes, there is another explanation," I hear some one say: "they may be explained by panmixia." Well, in the first place, as the explanation by panmixia implies that these gradations of perceptiveness have been arrived at by the dwindling of nervous structures, there lies at the basis of the explanation an unproved and improbable assumption; and, even were there no such difficulty, it may with certainty be denied that panmixia can furnish an explanation. Let us look at its pretensions.
It was not without good reason that Bentham protested against metaphors. Figures of speech in general, valuable as they are in poetry and rhetoric, can not be used without danger in science and philosophy. The title of Mr. Darwin's great work furnishes us with an instance of the misleading effects produced by them. It runs:—The Origin of Species by means of Natural Selection, or the preservation of Favored Races in the Struggle for Life. Here are two figures of speech which conspire to produce an impression more or less erroneous. The expression "natural selection" was chosen as serving to indicate some parallelism with artificial selection—the selection exercised by breeders. Now selection connotes volition, and thus gives to the thoughts of readers a wrong bias. Some increase of this bias is produced by the words in the second title, "favored races;" for anything which is favored implies the existence of some agent conferring a favor. I do not mean that Mr. Darwin himself failed to recognize the misleading connotations of his words, or that he did not avoid being misled by them. In chapter iv of the Origin of Species he says that, considered literally, "natural selection is a false term," and that the personification of Nature is objectionable; but he thinks that readers, and those who adopt his views, will soon learn to guard themselves against the wrong implications. Here I venture to think that he was mistaken. For thinking this there is the reason that even his disciple, Mr. Wallace—no, not his disciple, but his co-discoverer, ever to be honored—has apparently been influenced by them. When for example, in combating a view of mine, he says that "the very thing said to be impossible by variation and natural selection has been again and again effected by variation and artificial selection"; he seems clearly to imply that the